Ac power changeover

ABSTRACT

A power changeover circuit for selectively connecting an electrical load to one of two available power sources, preferably alternating current sources, wherein one of the sources constitutes an engine driven generator requiring a predetermined time to reach specified output characteristics after energization. Relay operated changeover switch means selectively connects the load to either of the electrical power sources, and second switch means in series with the changeover switch located between the changeover switch and the engine driven power source delays connected of the generator source with the load after disconnection of the load from the other source until the generator output reaches specified characteristics. Further, the circuit provides for the disconnection of the load from the generator upon deenergization of the generator, and prior to the changeover switch connecting the load to the other supply source in order to prevent arcing. Relays, resistors and time delay switch devices are utilized in the circuit to provide the desired operation.

United States Patent [191 Pittet 11] 3,808,451 Apr. 30, 1974 AC POWERCHANGEOVER Rene E. Pittet, Marshall, Mich.

[73] Assignee: Progressive Dynamics, Inc.,

Marshall, Mich.

[22] Filed: Nov.- 13, 1972 [21] Appl. No.: 305,665

[75] Inventor:

3,647,997 3/1972 Nerem 200/50 C Primary Examiner-Robert K. SchaeferAssistant Examiner-M. Ginsburg Attorney, Agent, or FirmBeaman & Beaman[57] ABSTRACT A power changeover circuit for selectively connecting anelectrical load to one of two available power sources, preferablyalternating current sources, wherein one of the sources constitutes anengine driven generator requiring a predetermined time to reachspecified output characteristics after energization. Relay operatedchangeover switch means selectively connects the load to either of theelectrical power sources, and second switch means in series with thechangeover switch located between the changeover switch and the enginedriven power source delays connected of the generator source with theload after disconnection of the load from the other source until thegenerator output reaches specified characteristics. Further, the circuitprovides for the disconnection of the load from the generator upondeenergization of the generator, and prior to the changeover switchconnecting the load to the other supply source in order to preventarcing. Relays, resistors and time delay switch devices are utilized inthe circuit to provide the desired operation.

9-Claims, 2 Drawing Figures AC POWER CHANGEOVER BACKGROUND OF THEINVENTION The invention pertains toelectrical changeover circuitswherein an electrical load is alternately connected to one of two powersupply sources.

Electrical changeover circuits have been widely used in emergencysystems wherein the electrical load is normally connected to a primarypower supply, but is automatically switched to an auxiliary emergencypower supply in the event of failure of the primary power source. Also,such circuits are commonly employed in the marine arts where vessels mayemploy a plurality of generators driven from the ships main turbines,and auxiliary generator systems are connected to the propeller driveshaft. Conventional circuits of the above type may be found in U.S. Pat.Nos. 1,777,845, 2,911,541, 3,243,598 and 3,317,741.

In the usual electric power changeover circuit switching takes placebetween a primary electric power supply and either a generator orbattery auxiliary power source, and relays, and similar electricalcomponents are utilized to automatically produce the switching from onepower source to the other upon failure of the primary source to energizethe circuit. However, known changeover circuits have not met the needsof electrical systems utilizing primary supply sources and engine drivengenerator supply sources wherein the primary source is automaticallydisconnected from the load upon energization of the generator whereinsuch transfer of electrical power does not take place until thegenerator has achieved predetermined power output characteristics.Additionally, known changeover circuits do not provide a switchingsequence which eliminates arcing, nor substantially eliminate otherdeleterious effects attendant with changeover circuit systems. I

Recreational vehicles, such as motor homes, large campers and traveltrailers, and also pleasure watercraft, often include small generatingequipment in order to permit the vehicle or boat to be self-sufficientfrom a power standpoint when utility supplied primary or shoreline poweris not available. Recreational vehicles and watercraft are increasinglyutilizing 110 volt AC systems, and by the use of power converters both12 volt and l 10 volt appliances and lighting circuits arecommonlyemployed. The use of auxiliary 110 volt AC generators onrecreational vehicles and watercraft is becoming increasingly common.

Currently, with recreational vehicles and watercraft utilizing 110 voltAC generators, a foolproof switchover system is utilized to preventstarting of the generator when the primary power source is connected tothe load system. Such foolproof changeover apparatus includes a powercord which must be removed from one receptacle and physically pluggedinto another, and

such changeover requires that the operator physically change theconductor from one receptacle to another, which takes place exteriorlyof the vehicle, resulting in considerable inconvenience, and danger dueto electric shock, particularly during inclement weather. Situationsarise where the shifting from a primary power supply to the enginedriven supply may occur rather frequently, and the troublesome procedureinvolved in shifting from one supply to another leaves much to bedesired. Also, with known changeover systems it is possible to imposereduced voltage upon the vehicle load system during starting of thegenerator prior to the generator reaching its full operating capacity,and such reduced voltages canv damage some electrical components, suchas motors, and if protection means are not incorporated into thegenerator circuit there is the possibility of serious damage occurringto the electrical equipment of the vehicle or watercraft due to relaychatter.

' SUMMARY OF THE INVENTION It is an object of the invention to providean electrical changeover system selectively connecting at least twopower sources to a load, wherein one of the power sources includes anengine driven generator, such that the changeover is automaticallyaccomplished from a primary supply to the generator supply uponenergization of the generator, and upon the generator substantiallyachieving designed output.

A further object of the invention is to provide an automatic changeovercircuit for use with a load selectively powered from two power sourceswherein sufficient time interval exists between transferring from onesource to the other to prevent arcing switch contacts.

In the practice of the invention a two pole changeover switch isinterposed between the load and the two power sources. At one positionof the switch both the active and neutral wires of one power source areconnected to the active and neutral conductors of the load. At the otherposition of the changeover switch the neutral and active wires of theload are connectible with the neutral and active conductors of theengine driven generator, however, a second switch is interposed inseries between the changeover switch and the generator controllingenergization of the load from the generator so that the load is notconnected to the generator until the generator has reached sufficientoutput to assume the load and provide the proper voltage.

Also, the second switch has such operating characteristics as to openprior to shifting of the changeover switch upon deenergization of thegenerator. When the engine driving the generator is stopped, the voltagedecay of the generator is first sensed by the second switch breaking thecircuit to the changeover switch, and upon the voltage furtherdecreasing the changeover switch is operated thereby connecting the loadto the primary or shoreline supply after sufficient time has occurred toautomatically quench any arcs which might have been produced at thechangeover switch contacts.

Preferably, the power supplies are alternating current, and thechangeover circuit utilizes current rectifying components wherein theswitches are operated by DC relays. The use of DC relays preventschattering of the relays, especially during decaying and build up of thegenerator voltage, and are preferable over an AC relay which willchatter and vibrate under such circumstances.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned objects andadvantages of the invention will be apparent from the followingdescription and accompanying drawings wherein:

FIG. 1 is an illustration of an AC changeover circuit in accord with theinvention, the switches being shown 3 in the position connecting theload with the primary power source,

FIG. 2 is a partial view of the circuit'illustrating the switches in theposition for connecting the load to the generator power source.

DESCRIPTION OF THE PREFERRED EMBODIMENT It will be appreciated that thechangeover circuit of the invention may be utilized in a wide variety ofapplications wherein various types of power sources may be utilized. Forinstance, while it is expected that the invention will find its primaryarea of utilization in conjunction with recreational vehicles andwatercraft, the circuit may be utilized in any instance wherein aplurality of power sources are alternately used to energize a load, oneof the power sources constituting an engine driven generator.

In FIG. 1 the primary power source is represented at 10, and includes anactive conductor 12, a neutral conductor l4, and a ground conductor 16.Ground conductors are also utilized with the generator, and load .andare illustrated, but not hereinafter mentioned. Usually, the supply willbe I 10 volts AC, as is conventionally available at parks, camp groundsand marinas for connection to recreational vehicles and watercraft.

The other source of alternating current is the engine driven generatorrepresented at 18 having an active output conductor 20, and a neutralconductor 22. The generator 18 has an operating output of 1 10 volts,and as used with recreational vehicles and small watercraft, thegenerator will be driven by a one or two cylinder internal combustionengine usually having a rating less than 20 horse power.

The load is represented at 24, and in the case of a recreational vehicleor watercraft, would consist of the complete 1 10 volt circuit of thevehicle or vessel. With recreational vehicles and watercraft it iscommon to supply 1 10 volt AC to a converter having a 12 volt DC output,which is also connected to a 12 volt battery. Many of the appliances ofrecreational vehicles and vessels are capable of operating on l2 volt DCsuch as lighting, refrigerators, etc., but it is also common to have 110volt appliances, such as air conditioners, directly connected. to the110 volt load. The load includes an active conductor 26 and a neutralconductor 28.

The two pole changeover switch 30 includes terminals to which'theprimary supply conductors 12 and 14 are attached, and includes terminalsto which conductors 32 and 34 are attached. The blades of the changeoverswitch 30 are operated by a relay coil 36, and in the normal positionthe switch 30 is closed, as represented in FIG. 1, establishingconnection between the conductors of the primary alternating currentsupply 10 and the load 24.

A two pole switch 38 is connected to the generator active and neutralconductors 20 and 22, and includes terminals to which conductors 32 and34 are connected. This switch is normally open, and is controlled by arelay coil 40. As the switch 38 is normally open, the connection betweenthe changeover switch 30 and the generator 18 is normally open, and itwill be therefore appreciated that both switches 30 and 38 must beenergized in order to complete the circuit between the generator and theload.

4 I It is desired that the switch relays 36 and 40 be operated by directcurrent, and for this purpose a full wave rectifier circuit generallyindicated at 42 is connected to the generator output conductors20 and22, and provides direct current at the rectifier output conductors 44and 46.

The relay coil 36 is directly connected to the output of the rectifier42, and thus energization of the relay coil occurs immediately uponvoltage being produced in the conductors 20 and 22 by the generator 18.Upon the voltage reaching a sufficient value the electromagnetic forcesdeveloped within the coil 36 shift the changeover switch 30 from thepositionshown in FIG. 1, to the position in FIG. 2 forestablishingconnection between the load and the generator.

The relay coil 40 is connected in series with resistance 48 which may beof 1,000 ohms, and is also in series with a time delay switch 50 havinga heating element represented at 52. The switch 50 has a 45 second delaybetween energization and actuation.

By way of example, the relay switch 30 may comprise a Potter andBrumfield PM 17DY relay, while relay switch 38 may comprise a Potter andBrumfield Model PRll DGO. The time delay switch 50 may be a- ,KlixonPN60700A1-2, 1 amp.

Operation of the described circuit is as follows:

Assuming the load 24, as represented by the electrical system of arecreational vehicle or boat, is at a location where a primary supply ofalternating current is available, the switches 30 and 38 will be in thecondition shown in FIG. 1, and the load 24 will be directly receivingits electricity from the primary supply 10. The load is completelydisconnected from the generator l8, and the contacts of switch 38 areopen.

If, while the primary power source is still connected, the operatorstarts the generator 18 by starting the internal combustion enginepowering the generator, the rotation of the generator will produce analternating current potential in the active conductor 20 therebyenergizing the rectifier circuit 42 to produce a direct currentenergizing the relay coil 36 shifting the changeover switch to theposition shown in FIG. 2. Operation of the switch 30 disconnects theload 24 from both the active and neutral conductors of the primary powersource 10, and connects the load to the conductors 32 and 34. However,as the switch 38 is still open the load is not connected to thegenerator 18, and thus is not en'- ergized from the generator. At thistime the recre ational vehicle lighting, and other 12' volt applianceswill be energized automatically from a battery source.

The generator 18 increases from O to volts in approximately 4 seconds ata rate of 30 volts per second. Thus, at approximately one second afteroperation of the generator, sufficient voltage is produced to energizerelay 36 to shift the changeover switch to the position shown in FIG. 2.

Forty-five seconds after the generator 18 has reached its maximum outputthe time delay switch element '52 will have heated sufficiently to causethe time delay switch 50 to close thereby energizing the relay coil 40through the resistor 48. Energization of the relay coil 40 closes switch38 establishing a completed circuit between the generator 18 and theload 24 permitting the load to be solely energized by the generator, andthe battery supply will automatically be disconnected by the convertercircuitry, not shown.

causes the relay switch 38 to release breaking the circuit between thegenerator and the load. The presence of the resistor 48 produces arelease or actuation of the relay switch 38 prior to theiactuation ofthe changeover relay switch 30.

Approximately 4 seconds after the generator 18 is de-energized thevoltage has decayed sufficiently to permit the relay switch 30 to shift,again positioning the switch 30 as shown in FIG. 1, reestablishingelectrical connection between the primary power supply and the load 24.i

The sequential operation of the switches 30 and 38 has several purposes.First, when initially energizing the generator 18, the primary supply 10will be disconnected from the load, yet the presence of the switch 38prevents the partial voltage developed by the generator while attainingoperating speed from being imposed on the load, and thereby possiblydamaging electric motors, or other components constituting the load.Also,

the generator is able to attain maximum output quickly under no loadconditions.

Secondly, when the generator motor has been deenergized, and the voltagegenerated thereby is decaying, the fact that the switch 38 breaks thecircuit between the generator and the load prior to the changeoverswitch connecting the load to the primary supply prevents arcing attheswitch contacts, resulting in increased'switch life, and elimination ofthe deleterious effects of switch arcing and relay chatter.

The switch 38 could be a single pole type connecting conductors 20 and32, and conductor 22 could directly connect to a terminal at switch 30.Such a single pole switch is the most economical arrangement, and servesthe desired purposes as described above.

FIG. 1 illustrates a circuit device for a amp. load using a generatorcapable of producing a 30 amp. output. If the load is ofa 60 amp.requirement, a 60 amp.-

generator is employed, and two 30 amp load circuits are employed. insuch'event a duplicate set of contacts similar to those changeovercontacts of switch 30 are employed also operated by the coil 36, andwiring par allel to that illustrated is used such that both loadcircuits are simultaneously changed over from one power source to theother, and the switch 38 is connected in series with active conductorsfrom the load circuits to the generator active conductor.

It will be appreciated that various similar modifications may beapparent to those skilled in the art without departing from the spiritand scope of the invention.

What is claimed is:'

1. An electrical power changeover system comprising, incombination, afirst supply of electrical current, a second supply of electricalcurrent constituting an operator controlled engine driven generator, anelectrical load, first switch means normally electrically connectingsaid load to said first supply and operable to connect said load to saidsecond supply and disconnect said load from said first'supply, secondswitch means in series with said first switch means between said firstswitch means and said second supply selectively controlling energizationof said first switch means from said second supply, first switch controlmeans controlling said first switch means in dependence upon the outputof said second supply, second switch control means controlling saidsecond switch means in accord with operation of said second supply, andmeans controlling at least one of said switch control means whereinsaidswitch means operate at different times such that said load is notenergized from said second supply until the load is disconnected fromsaid first supply and said second supply attains predetermined voltagecharacteristics, and said load being disconnected from said secondsupply during de-energizing of said second supply prior to beingconnected to said first supply by a time interval sufficient to preventarcing at said first switch means.

2. Anelectrical power changeover system comprising, in combination, afirst supply of electrical current, a second supply of electricalcurrent constituting an operator controlled engine driven generator, anelectrical load, a first switch selectively electrically connecting saidload to said first and second supplies and normally connecting said loadto said first supply, a second normally open switch electricallyinterposed between said second supply and said first switch in serieswith said first switch, first control means operating said first switchupon-energization of said second supply to permit connection of saidload to said second supply, and second control means closing said secondswitch after a predetermined time interval after energization of saidsecond supply to connect said load to said second supply and openingupon de-energization of said second supply and prior to operation ofsaid first switch to connect said load to said first supply.

3. An electrical power changeover system as in claim 2 wherein saidsecond control means includes time delay means delaying operation ofsaid second switch a predetermined time interval after energization ofsaid engine driven generator.

4. An electrical power changeover system as in claim 2 wherein saidsecond control means includes an electromagnetic relay and a resistancein series with said relay causing de-energizing of said relay andopening of said second switch at a higher voltage output of said secondsupply than the voltage required to operate said first control means toopen said first switch. 7

5. An electrical power changeover circuit comprising, in combination, afirst supply of electrical current having an active conductor and aground conductor, a second supply of electrical current having an activeconductor and a ground conductor comprising an operator controlled motordriven generator, a load having active and ground conductors, firstrelay switch means controlled by said second supply for selectivelyconupon the output of said motor driven generator falling below theoperating voltage of said first relay switch means, second switch meanslocated in at least one of said conductors of said second supply ofelectrical current, and means energized from said second supply closingsaid second switch means upon said motor 7 driven generator secondsupply attaining a predetermined voltage output upon being energized andopening said second switch means upon said motor driven generator beingde-energized and prior to said first switch means disconnecting saidload conductors from said second supply conductors.

6. In an electrical power changeover circuit as in claim wherein saidmeans opening and closing said second switch means comprises a timedelay switch controlling said second switch means.

7. In an electrical power changeover circuit as in claim 6, a resistorin series with the circuit of said time delay switch causing said secondswitch means to open prior to operation of said first switch means toconnect ond switch relay to said rectifying means output.

1. An electrical power changeover system comprising, in combination, afirst supply of electrical current, a second supply of electricalcurrent constituting an operator controlled engine driven generator, anelectrical load, first switch means normally electrically connectingsaid load to said first supply and operable to connect said load to saidsecond supply and disconnect said load from said first supply, secondswitch means in series with said first switch means between said firstswitch means and said second supply selectively controlling energizationof said first switch means from said second supply, first switch controlmeans controlling said first switch means in dependence upon the outputof said second supply, second switch control means controlling saidsecond switch means in accord with operation of said second supply, andmeans controlling at least one of said switch control means wherein saidswitch means operate at different times such that said load is notenergized from said second supply until the load is disconnected fromsaid first supply and said second supply attains predetermined voltagecharacteristics, and said load being disconnected from said secondsupply during de-energizing of said second supply prior to beingconnected to said first supply by a time interval sufficient to preventarcing at said first switch means.
 2. An electrical power changeoversystem comprising, in combination, a first supply of electrical current,a second supply of electrical current constituting an operatorcontrolled engine driven generator, an electrical load, a first switchselectively electrically connecting said load to said first and secondsupplies and normally connecting said load to said first supply, asecond normally open switch electrically interposed between said secondsupply and said first switch in series with said first switch, firstcontrol means operating said first switch upon energization of saidsecond supply to permit connection of said load to said second supply,and second control means closing said second switch after apredetermined time interval after energization of said second supply toconnect said load to said second supply and opening upon de-energizationof said second supply and prior to operation of said first switch toconnect said load to said first supply.
 3. An eleCtrical powerchangeover system as in claim 2 wherein said second control meansincludes time delay means delaying operation of said second switch apredetermined time interval after energization of said engine drivengenerator.
 4. An electrical power changeover system as in claim 2wherein said second control means includes an electromagnetic relay anda resistance in series with said relay causing de-energizing of saidrelay and opening of said second switch at a higher voltage output ofsaid second supply than the voltage required to operate said firstcontrol means to open said first switch.
 5. An electrical powerchangeover circuit comprising, in combination, a first supply ofelectrical current having an active conductor and a ground conductor, asecond supply of electrical current having an active conductor and aground conductor comprising an operator controlled motor drivengenerator, a load having active and ground conductors, first relayswitch means controlled by said second supply for selectively connectingsaid load active and ground conductors to said active and groundconductors, respectively, of said first and second supplies ofelectrical current, said first relay switch means normally connectingsaid load conductors to corresponding conductors of said first supply,and connecting said load conductors to corresponding conductors of saidsecond supply upon energizing of said motor driven generator anddisconnecting said load conductors from said second supply conductorsupon the output of said motor driven generator falling below theoperating voltage of said first relay switch means, second switch meanslocated in at least one of said conductors of said second supply ofelectrical current, and means energized from said second supply closingsaid second switch means upon said motor driven generator second supplyattaining a predetermined voltage output upon being energized andopening said second switch means upon said motor driven generator beingde-energized and prior to said first switch means disconnecting saidload conductors from said second supply conductors.
 6. In an electricalpower changeover circuit as in claim 5 wherein said means opening andclosing said second switch means comprises a time delay switchcontrolling said second switch means.
 7. In an electrical powerchangeover circuit as in claim 6, a resistor in series with the circuitof said time delay switch causing said second switch means to open priorto operation of said first switch means to connect said load conductorsto said first supply conductors.
 8. In an electrical power changeovercircuit as in claim 5 wherein said first and second supplies ofelectrical current provide alternating current, current rectifying meansconnected to said second supply producing a direct current output, saidfirst relay switch means being connected to said rectifying meansoutput.
 9. In an electrical power changeover circuit as in claim 8wherein said second switch means comprises a relay, and conductorsselectively connecting said second switch relay to said rectifying meansoutput.